A conventional projection display requires a projection unit to be adjusted in six degrees of freedom individually so that an image out of the projection unit is projected in alignment with a screen without distortion. Japanese Patent Application Laid-Open No. 2004-347743 (pp. 3-9, FIG. 1) discloses a projection display achieving adjustments in three translational degrees of freedom and three rotational degrees of freedom by mechanical operations of an image-outline adjusting mechanism, thereby positioning a projection unit in six degrees of freedom in total. Japanese Patent Application Laid-Open No. 11-341403 (1999) (pp. 3-5, FIG. 1) discloses a projection display capable of achieving adjustments in degrees of freedom by processing an image signal, so that an image to be projected is adjusted.
For achieving mechanical adjustments in six degrees of freedom by an image-outline adjusting mechanism as disclosed in the above-mentioned JP2004-347743, a moving panel for each degree of freedom, i.e., a total of six moving panels or rotating panels are required. This increases the number, mass and costs of components. In such image-outline adjusting mechanism, the largest number of components is used particularly for an adjusting part along the z-axis extending in the front-to-rear direction relative to the screen, making the z-axis adjustment difficult. The z-axis adjustment thus requires much time, and is most likely to cause displacements in image outline due to shakes or, drops during transportation of products.
In contrast, electric image-outline adjustments by processing an image signal to be input to a projection unit as disclosed in the above-mentioned JP11-341403 (1999) reduces the number, mass and costs of components. However, a rotational distortion or trapezoidal distortion on the screen, if any, is difficult to be corrected by signal processing; even if it is not impossible, a displayed image is significantly degraded in quality.